Diesel combustion may generate emissions, including particulate matter (PM). The particulate matter may include diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, PM can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometer range of 100 nanometers. Various technologies have been developed for identifying and filtering out exhaust PMs before the exhaust is released to the atmosphere.
As an example, soot sensors, also known as PM sensors, may be used in vehicles having internal combustion engines. A PM sensor may be located upstream and/or downstream of a diesel particulate filter (DPF), and may be used to sense PM loading on the filter and diagnose operation of the DPF. Typically, the PM sensor may sense a particulate matter or soot load based on a correlation between a measured change in electrical conductivity (or resistivity) between a pair of thin electrodes placed on a planar substrate surface of the sensor with the amount of PM deposited between the measuring electrodes. Specifically, the measured conductivity provides a measure of soot accumulation.
An example PM sensor is shown by Goulette et. al. in US 2015/0153249 A1. Therein, a conductive material disposed on a substrate is patterned to form interdigitated “comb” electrodes of a PM sensor. When a voltage is applied across the electrodes, soot particles are accumulated at or near the surface of the substrate between the electrodes.
The inventors herein have recognized potential issues with such systems. As an example, in such PM sensors, only a small fraction of the PM in the incoming exhaust experiences the electrostatic forces exerted between the electrodes and gets collected across the electrodes formed on the surface of the sensor, thereby leading to low sensitivity of the sensors. Further, even the fraction of the PM that is accumulated on the surface may not be uniform due to a bias in flow distribution across the surface of the sensor. The non-uniform deposition of the PM on the sensor surface may further exacerbate the issue of low sensitivity of the sensor. The inventors have recognized the above issues and identified an approach to at least partly address the issues. In one example, the issues above may be addressed by a sensor assembly, comprising rows of flow guides arranged between a front surface and a rear surface of the assembly, each flow guide having a positive electrode and a negative electrode formed along opposite surfaces of the flow guide, a plurality of gaps formed between the flow guides, and multiple projections arranged between a top surface and a bottom surface of the assembly, the multiple projections aligned between the plurality of gaps. In this way, by aligning each projection in the gap formed between two adjacent flow guides, soot particles in the exhaust may be pushed further into the gap and closer to the electrodes formed across the gap. Therefore, the probability of capture of the soot particles in the gap across the electrodes is increased and thus, the sensitivity of the sensor assembly to capture soot particles in the exhaust passage is increased.
As one example, an exhaust PM sensor assembly may be positioned downstream of an exhaust particulate filter in an exhaust passage. The PM sensor assembly may be a box-type sensor including rows of flow guides that are arranged inside the sensor assembly. Specifically the sensor assembly may include sealed bottom, top, and side surfaces, and further include open front, and rear surfaces, for directing exhaust inside and out of the assembly. Within the assembly, rows of flow guides may be arranged transversely between the front and the rear surface. Herein, the flow guides may include rectangular blocks separated by a gap extending longitudinally between the side surfaces. In addition, the rectangular blocks may include positive and negative electrodes formed along two different, yet parallel side surfaces of the rectangular blocks. In one example, the rectangular blocks may be arranged such that the positive electrodes of all the rectangular blocks face towards the front surface of the assembly and the negative electrodes of all the rectangular blocks face towards the rear surface of the assembly. In such an example, soot accumulation may occur in the gap between the rectangular blocks where the positive electrode of each rectangular block faces the negative electrode of the neighboring rectangular block. Additionally, the assembly may include projections arranged between the top surface and the bottom surface of the assembly. Herein, the projections may be aligned with respect to the gap between the blocks. Specifically, the projections may be configured to direct the soot particles closer into the gap and trap the particles inside the gap for a longer time, thereby allowing the soot particles to be closer to the electrodes for a longer time. Thus, the probability of soot capture in the gap across the electrodes is increased. In one example, triangular prism shaped projections may be included. Herein, the technical effect of including the projections is to exert a mechanical force on the incoming soot particles and push them closer to the electrodes where the soot particles may experience a greater electrostatic force. In this way, more of the incoming soot particulates may be captured by the sensor assembly. In another example, the projections may include triangular shields that may be configures to circulate the soot particulates for a longer duration in the region enclosed within the triangular shields, specifically in the gap between the electrodes, thereby increasing the amount of particulates captured across the electrodes in the gap. Overall, these characteristics of the sensor assembly may cause an output of the sensor assembly to be more accurate, thereby increasing the accuracy of estimating particulate loading on a particulate filter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.